Halomethylation of aromatics is a well established reaction. However, halomethylation of phenols is generally not a selective process. In general, it is difficult to obtain monomeric chloromethylated products. See, G. A. Olah, Friedel-Crafts and Related Reactions, Vol. II, Part 2, pp. 701-11, 1964. Halogenation of alkylphenols is normally accompanied by side-reactions. V. V. Ershov, A. A. Volodkin & G. N. Bogdanov, Russion Chemical Reviews, 32, 75-93 (1963). Furthermore, bromomethylation, in general, affords lower yields than chloromethylation, ibid., pp. 734-735.
The preparation of a halogenated phenol such as 4-bromomethyl-3, 5-dibromo-2, 6-dimethylphenol (tribromomesitol) can involve the following sequence: bromination of 2, 4, 6-trimethylphenol (mesitol) with 2 moles of bromine in acetic acid to prepare 3, 5-dibromo-2, 4, 6-trimethylphenol (dibromometisol) which is isolated by precipitation with water. K. Auwers & F. Rapp, Ann., 302, 153-71 (1898) and O. Jacobsen, Ann., 195, 265-92 (1879); the dibromomesit 1 is brominated in acetic acid sodium acetate buffer at low temperatures to afford an intermediate, 3, 4, 5-tribromo-2, 4, 6-trimethyl-2, 5-cyclohexadienone, which is isolated by fast precipitation with water and filtration; this solid slowly rearranges to tribromomesitol at room temperature, more quickly at higher temperatures. K. Fries & E. Brandes, Ann., 542, 48-77 (1939). This procedure to prepare tribromomesitol is complex and not industrially viable.
A more direct method of preparation of tribromomesitol involves the reaction of mesitol in glacial acetic acid with an excess of bromine, using 10.6 moles of bromine per mole of mesitol. The yields are 66 percent and the product isolation is difficult. K. Auwers and H. Allendorff, Ann., 302, 76-98 (1898). This procedure is not industrially viable either.
Chlorination of 3, 5-dichloro-2, 4, 6-trimethylphenol in trifluoroaoetic acid is known to produce 3, 4, 5-trichloro-2, 4, 6-trimethyl-2, 5-cyclohexadienone or 3, 5, 6-trichloro-2, 4, 6-trimethyl-2, 4-cyclohexadienone. Antinori et al., J. Chem. Soc. (B), 373-77 (1969).